The practice of polymerizing phosphorylcholine group-containing monomers for use as a contact lens material is a prior art (Patent Documents 1-3). For example, Patent Document 1 discloses a moist soft contact lens containing a phosphorylcholine group-containing (meth)acrylic ester as a constitutional unit; it is described as having superior moisture content, oxygen permeability, and tensile strength, as well as reduced protein adsorption and the ability to suppress stain adhesion.
As an example of an after-treatment method for contact lenses, Patent Document 4 describes polymerization of phosphorylcholine group-containing monomers on the contact lens surface to prepare a contact lens having hydrophilic surfaces and reduced protein adsorption.
In addition, Patent Document 5 describes a reduction in protein adsorption by chemically bonding a low molecular weight phosphorylcholine compound onto the contact lens surface.
That is, Example 5 of Patent Document 5 claims that the adhesion of albumin and lysozyme onto a contact lens can be suppressed by treating a 4-hydroxyethyl methacrylate-co-methacryl acid copolymer contact lens with 2-[{2-(1-imidazolecarbonyloxyethoxy)hydroxyphosphinyl}oxy]-N,N,N-trimethyletanaminiumnitroxide inner salt.
However, the method described in Patent Document 5 uses a very cumbersome method with many steps, which makes it very hard to obtain the target substance with a high yield and high purity. Also, the reaction to introduce phosphorylcholine groups onto the contact lens surface, under the conditions described in these Patent Documents, does not proceed sufficiently and results in a low introduction level, and therefore a superior protein adsorption prevention effect is not achieved.
Stains on a contact lens result from adsorption of proteins and/or lipids contained in lacrimal fluid; these stains can cause eye troubles such as allergies and infections (Non-patent Document 1). Protein stains cause a fatal problem particularly for a moist contact lens whose main ingredient is a 2-hydroxyethyl methacrylate polymer, a highly moist soft contact lens prepared by copolymerizing this ingredient with a small amount of methacrylic acid, which is an ionic monomer, and a soft contact lens whose main ingredient is a polymer of a hydrophilic monomer such as N-vinyl pyrrolidone and N,N-dimethyl acrylamide.
Patent Document 1: Japanese Patent Laid-Open H10-177152 bulletin
Patent Document 2: Japanese Patent Laid-Open 2000-111847 bulletin
Patent Document 3: Japanese Patent Laid-Open 2000-169526 bulletin
Patent Document 4: Japanese Patent Laid-Open 2001-337298 bulletin
Patent Document 5: Japanese Patent Laid-Open H5-505121 bulletin
Non-patent Document 1: “Stains on soft contact lenses and analysis thereof”, Material Stage, Vol. 4, No. 1, 2004